1. Field of the Invention
The disclosure relates generally to cooling systems for computer systems and, more specifically, to a cooling system for reducing noise and improving volumetric output of the cooling system.
2. Description of the Related Art
While the recent increase in the speed of microprocessors has significantly increased the processing capability of computers, this increase in speed has resulted in additional heat being generated by the processor and/or other components within a computer system. Many of these components, including the processor, are adversely affected by high temperatures; and thus, a need exists for dissipating the excess heat. Typically, a heat sink is thermally attached to an integrated circuit package containing the processor or other chip, and a cooling fan is used to force air over the heat sink.
A rapidly growing area of interest for customers of computer systems is acoustics or noise. Many customers place significant emphasis on the acoustical characteristics of a system in valuing the quality of the system. Currently, the primary elements operative in the production of system acoustical noise are the computer system's various electromechanical cooling fans, such as system fans, microelectronic component fans, and power supply fans.
An issue associated with current fans involves striking a balance between improving volumetric output through the cooling fan (i.e., increased cooling) and reducing the acoustical output of the fan. Although solutions currently exist to increase the output through the cooling fan, these solution negatively affect the acoustics of the fan. For example, increasing the speed (i.e., RPM) of the cooling fan increases acoustical output. Adding flow straighteners to the exhaust of the cooling fan, which turn airflow “swirl” energy into potential pressure drop energy, is another example, but the flow straighteners also increase acoustical output.
FIGS. 1 and 2 respectively illustrate the presumed (FIG. 1) and actual (FIG. 2) flow of fluid F exiting a conventional cooling fan 210. Although a common presumption is that fluid F exits the fan 210 at a vector normal to a frame 220 of the fan 210 or parallel to a rotational axis RA of the fan 210, this is not correct. As known to those experienced in fans and/or fluid aerodynamics, the actual characteristics of fluid F exiting the fan 210 differ significantly from the characteristics shown in FIG. 1.
As illustrated in FIG. 2, the actual vector of fluid F exiting the fan 210 is at a angle that away from the rotation axis RA of the fan 210. This angle can be 45° or even greater. The angled vector of fluid F exiting the fan 210 results from fluid radially moving away from the hub 212 and along the surfaces of the fan blades. The exact angle the fluid exits the fan 210 depends upon several known factors, such as the pitch angle and shape of the blades.
A conventional cooling fan 110 and shroud 120 and how fan noise is created is illustrated in FIG. 3. The conventional fan 110 includes blades 114, each having an outer periphery 118 that is substantially parallel to a rotational axis RA of the fan 110. The shroud 120 surrounds, in part, the blades 114, and a substantially constant width gap separates the periphery 118 of the fan blades from the shroud 120. Since the fluid F exits the outer periphery 118 at an angle relative to the rotational axis RA, the fluid F impacts the shroud 120, which reflects the fluid F back into the fan 110.
The turbulence or swirl created in the fluid F causes the shroud 120 to vibrate, thus creating acoustical emissions from the fan/shroud assembly. The turbulence within the fluid F also acts as in impedance to the fluid F through the fan 120, which reduces the maximum volumetric output of fluid F of the fan 120. The impingement of the fluid F on the shroud 120 also increases the resistance of fluid F through the fan 120. There is, therefore, a need to improve the volumetric output of fluid through a cooling fan while at the same time reducing the acoustical output of the fan.